feat(physics): C4 route 2 — ForcePosition through the canonical placement

A local-player ForcePosition had TWO independent writers for one accepted
packet: LocalForcePositionTransaction snapped the physics body
(PlayerMovementController.BlipPosition, a raw SnapToCell with no collision
resolve), while LiveEntityNetworkUpdateController's generic tail separately
wrote position/cell/rotation to the render WorldEntity from the raw wire and
rebucketed it. Two stores, one packet — the divergence class 670f307c fixed on
the remote path. The outbound AutonomousPosition ack also fired BEFORE any
canonical commit existed: we told ACE "got it, I'm here" before deciding where
"here" was, and the trailing isCurrent() could only suppress the continuation,
never recall the packet.

RuntimeAcceptedPositionDriveController is now the one Runtime-owned seam. Both
hosts call the identical TryExecuteAcceptedLocalPosition; App and headless
project the committed result through the existing placement projection sink
(LiveEntityRuntime.TryApplyRuntimePlacementPlace already performed the same
four writes, from committed state rather than a wire guess).

Retail: SmartBox::HandleReceivedPosition @0x00453FD0's FORCE_POSITION branch is
get_heading -> Frame::set_heading -> SmartBox::BlipPlayer @0x00453940 -> stamp
POSITION_TS -> SendPositionEvent @0x00454091 -> return @0x0045409D. BlipPlayer
is CPhysicsObj::SetPositionSimple @0x005162B0 with flags 0x1012
(Teleport|Slide|SendPositionEvent) — a real collision-resolving SetPosition,
not a snap. The pinned classifier already encoded this exactly.

Named behaviour changes:

* The ack is now an OUTPUT of the committed route, fired strictly after the
  canonical commit and exactly once per accepted force packet.
* The ForcePosition route no longer re-arms the constraint leash. The force
  branch returns at 0x0045409D, ahead of all three ConstrainTo sites
  (0x00454272, 0x0045418A, 0x004541EC); the old re-arm cited retail's "Player,
  normal" branch, which BlipPlayer is not on. The teleport, CommitPreparedPosition
  and first-entry callers legitimately still constrain and are untouched.
* A force correction that terminates WITHOUT committing still sends its
  position event and is not retried — retail's BlipPlayer discards
  SetPositionSimple's SetPositionError return and acks unconditionally.

A single _pending funnel owns the in-flight placement, deciding on the token's
PositionAuthorityVersion against the record's: equal -> clear; advanced with the
newest accepted event still a force -> re-issue, re-classified; advanced to an
ordinary Apply -> clear, since newer server truth owns that pose. This closes a
double-apply/double-ack and a silently-dropped correction that two earlier
iterations of this slice each introduced.

AD-62 records the residual: a ForcePosition our async collision publication
cannot carry to a committed placement is not re-applied. Retail has no park —
its world is fully resident and its placement synchronous — so the state is
unreachable there. AP-131 is NOT retired; its legacy Position caller is route 4.

Deleted: LocalForcePositionTransaction, PlayerMovementController.BlipPosition,
HeadlessSessionWorldProjection.BlipLocalPlayer.

Gates: complete Release solution 10,858 passed / 4 skipped / 0 failed (baseline
10,844/4/0). Two independent Opus reviews (retail-conformance and
architecture/adversarial) PASS on the final diff after three FAIL rounds; every
intermediate state was fully green, so the suite caught none of the four real
defects. Connected acceptance is NOT run: nothing a user can do makes ACE emit
a ForcePosition without retail's @pklite, which acdream does not implement — see
docs/research/2026-08-03-c4-route-2-visual-gate.md.

Known gap, recorded not claimed: the plan's acceptance item 2 is unmet. The App
double-write check is a source pin, and "the committed projection moves the
render entity" is uncovered at any layer (#292). Filed alongside: #286-#291,
#293-#296.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/AcDream.App/World/LiveEntityHydrationController.cs

@@ -189,6 +189,13 @@ internal sealed class LiveEntityHydrationController : ILiveEntityLandblockLoaded
     /// controller without one.
     /// </summary>
     private readonly RuntimeFirstEntryDriveController? _firstEntry;
+    /// <summary>
+    /// C4 route 2: the graphical accepted-Position drive controller — pumped
+    /// alongside <see cref="_firstEntry"/> so a ForcePosition parked awaiting
+    /// its destination collision generation resolves promptly. Optional for
+    /// the same reason <see cref="_firstEntry"/> is.
+    /// </summary>
+    private readonly RuntimeAcceptedPositionDriveController? _acceptedPositionDrive;
     private readonly Dictionary<RuntimeEntityRecord, CanonicalProjectionOperation>
         _projectionOperations =
             new(ReferenceEqualityComparer.Instance);
@@ -213,7 +220,8 @@ internal sealed class LiveEntityHydrationController : ILiveEntityLandblockLoaded
         LiveEntityDeletionController deletion,
         DormantLiveEntityStore? dormant = null,
         Action<string>? diagnostic = null,
-        RuntimeFirstEntryDriveController? firstEntry = null)
+        RuntimeFirstEntryDriveController? firstEntry = null,
+        RuntimeAcceptedPositionDriveController? acceptedPositionDrive = null)
     {
         _runtime = runtime ?? throw new ArgumentNullException(nameof(runtime));
         _entityObjects = entityObjects
@@ -230,6 +238,7 @@ internal sealed class LiveEntityHydrationController : ILiveEntityLandblockLoaded
         _dormant = dormant ?? new DormantLiveEntityStore();
         _diagnostic = diagnostic;
         _firstEntry = firstEntry;
+        _acceptedPositionDrive = acceptedPositionDrive;
     }
 
     internal event Action<uint>? AppearanceApplied;
@@ -403,6 +412,8 @@ AppearanceSynchronization:
             // destination cell, FIFO ahead of us) is retried by the
             // per-frame placement retry phase.
             _firstEntry?.DriveAll();
+            // C4 route 2: same pump for a parked ForcePosition.
+            _acceptedPositionDrive?.Advance();
         }
     }